Functional reconnections established by central respiratory neurons regenerating axons into a nerve graft bridging the respiratory centers to the cervical spinal cord.

The present work investigated, in adult rats, the long-term functional properties and terminal reconnections of central respiratory neurons regenerating axons within a peripheral nerve autograft bridging two separated central structures. A nerve graft was first inserted into the left medulla oblongata, in which the respiratory centers are located. Three months later, a C3 left hemisection was performed, and the distal tip of the graft was implanted into the C4 left spinal cord at the level of the phrenic nucleus, a natural central inspiratory target. Six to eight months after medullary implantation, the animals (n = 12) were electrophysiologically investigated to test 1) the phrenic target reinnervation by analyzing the phrenic responses elicited by bridge electrical stimulation and 2) the bridge innervation by unitary recordings of the spontaneous activity of regenerated axons within the nerve bridge. In the control group (n = 6), the medullary site of implantation corresponded to the dorsolateral medulla, a region known to be an unsuitable site for inducing respiratory axonal regrowth after nerve grafting. Stimulation of the nerve bridge never elicited phrenic nerve response, and no respiratory units were found within the nerve bridge. In the experimental group (n = 6), the proximal tip of the nerve bridge was implanted within the ventrolateral medulla at the level of the respiratory centers. Electrical stimulation of the nerve bridge induced phrenic nerve responses that reflected a postsynaptic activation of the phrenic target. Subsequent unitary recordings from teased fibers within the bridge revealed the presence of regenerated inspiratory fibers exhibiting discharge patterns typical of medullary inspiratory neurons, which normally make synaptic contacts with the inspiratory phrenic target. These results indicate that, when provided with an appropriate denervated target, central respiratory neurons with regenerated axons along a nerve bridge can remain functional for a long period and can make precise and specific functional reconnections with central homotypic target neurons.

[Cytomegalovirus seroepidemiology in the community of Madrid]. / Seroepidemiología frente a citomegalovirus en la Comunidad de Madrid.

BACKGROUND: Cytomegalovirus (CMV) is frequently asymptomatic. However, it constitutes an important cause of congenital disease and severe pathology in immunodepressed patients, thus representing an important problem in Public Health. The object of this work was to study the prevalence of IgG against CMV (IgG-CMV) in the general population from Madrid. METHODS: It is a transversal study, in which IgG-CMV was assayed in a representative sample of the general population from the Region of Madrid, aged 2 to 60 years (n = 2030). Participants were recruited by a two-stage cluster sample procedure from those attending primary health care centres between October, 1993 and February, 1994. For the statistical analysis the chi 2 and chi 2 lineal trend tests were employed. The percentages of seroprevalence and the specific odds ratios were calculated with confidence intervals of 95%. RESULTS: The overall seroprevalence has been 62.8% (IC95% 60.6-64.9), ranging from 58.4% (IC95% 55.2-61.5) in men to 66.7% (IC95% 63.7-69.5) in women. A significant association between increase of the age and increment of the seroprevalence was observed. The consult to dentistry, the antecedent of surgery, as well as tattooing and acupuncture has been identified as risk factors of acquiring the infection. On the other hand, to have carried out University studies seems to act as a significant factor of protection. CONCLUSIONS: Although the risk factors detected indicates a transmission by blood, the high prevalence suggests the existence of other more common ways. The age-dependent seroprevalence increase confirms an important number of infections in the adult age. However, it cannot be exclude that this increase responds to an effect cohort due to socio-economic improvements similar to the detected for other virus.

Assessment of U.S. helicopter emergency medical services' planning and preparedness for disaster response.

INTRODUCTION: Helicopter emergency medical services (HEMS) roles in disaster response vary significantly from routine operation, and as reported in the literature, such responses have not been without difficulty. We identified nine criteria (written policy, triage and incident command training disaster drill participation, ground and air communications plan, critical incident stress management, annual review, policy sharing) that may significantly affected an air medical program's disaster preparedness, response, and recovery. Of these criteria, a written policy is considered of primary importance. METHODS: A written survey was developed and mailed in July 1995 to 187 U.S. rotor-wing members of the Association of Air Medical Services. The survey was designed to identify the programs that had a written policy and fulfilled the guideline criteria, had a written policy and partially fulfilled the criteria, or did not have a written policy. RESULTS: Surveys were returned from 104 (56%) programs. Of the 103 qualifying respondents, 16 (16%) meet the criteria, 55 (53%) partially met the criteria, and 32 (31%) did not have written policies. CONCLUSION: Most U.S. HEMS programs have not fully addressed disaster preparedness, response, and recovery. HEMS disaster response guidelines should be established, and these criteria should be incorporated.

CNS axonal regeneration with peripheral nerve grafts cryopreserved by vitrification: cytological and functional aspects.

To test cool-warm protocols for storing peripheral nerves, 4-cm-long-nerve segments were removed from the hindleg of adult rats and cryopreserved using a vitrification solution (or cryoprotective mixture) containing a mixture of polyalcohols (2,3-butanediol, 1,2-propanediol, polyethylene glycol, and Belzer U.W. medium). Schwann cell viability and morphology were studied with regard to the effect of (i) cryoprotective mixture concentration (100, 50, and 30% diluted in human serum albumin at 4%), (ii) duration of exposure (10, 15, or 30 min in a single step) of nerves to the cryoprotective mixture, (iii) cooling rate (F1/F2, F3, and F4: 3, 12, and 231 degrees C/min, respectively), and (iv) type of replacement of cryoprotectant (T1, one step; or T2, perfusion) after warming. Nerves exposed 10 min to cryoprotective mixture 50% (2,3-butanediol, 1.926 mol.liter-1; 1,2-propanediol, 3.063 mol.liter-1; polyethylene glycol, 0.084 mol.liter-1; and Belzer U.W., 22.4 mosm-1) and cooled-warmed with the F2/F3/F4-T2 protocols contained live and correctly cryopreserved Schwann cells. The capacity of these cryopreserved nerve segments (n = 6) to be subsequently repopulated by regenerating axons from central neurons was compared to that of fresh nerves when used as peripheral nerve autografts implanted within the spinal cord at the level of the descending respiratory pathways. All cryopreserved nerve grafts were successfully reinnervated by regenerated central axons. Unitary spontaneous action potentials propagated along these axons were assessed by recording the discharge of tested nervous filaments (T) from the grafts in artificially ventilated and paralyzed animals. Out of 535 T, 32 (6 +/- 1.2%) presented spontaneous unitary activity with respiratory (R, n = 2) and nonrespiratory (NR, n = 30) pattern of discharge. The T mean number, the occurrence rate referenced to the total number of T (R/T, NR/T, and R + NR/T) and the mean number of spontaneous units (R, NR, R + NR) were compared to those of fresh spinal peripheral nerve grafts. Except for T, cryopreserved peripheral nerve grafts contained statistically significantly (P < 0.05) less spontaneous R and NR unitary activity, which represented, respectively, 6.2 +/- 6.2 and 26.8 +/- 5.7% of that found in the control group. These data indicate that nerves cryopreserved with the protocols described above contain viable Schwann cells which constitute a suitable support to induce regeneration of central fibers. The effectiveness of nerve cryopreservation by vitrification is discussed with regard to Schwann cell viability following cool-warm protocols and to subsequent reinnervation of the cryopreserved peripheral nerve grafts.

Investigation of bone developmental and histopathologic changes from intraosseous infusion.

STUDY OBJECTIVE: To evaluate clinical and cellular changes of bone through the rapid growth phase of development after intraosseous infusion of hypertonic or isotonic solutions at slow or fast infusion rates in a pig model. METHODS: This was a prospective, randomized, partially blinded, comparative study using a porcine model in an urban teaching hospital laboratory with further development in a local farm environment. Sixty pigs weighing 12 to 30 kg were anesthetized and endotracheally intubated, and a no. 15 Jamshidi bone marrow needle was inserted into a front forelimb. Hypertonic (mannitol) or isotonic (saline) solutions of 8 mL/kg were infused through the intraosseous site at a rapid or slow infusion rate. Animals were observed for approximately 6 months, after which they were killed and the front forelimbs harvested for gross pathologic and histologic evaluation. RESULTS: No clinical complications were noted in any of the animal groups. No substantial histologic differences were found between the hypertonic and isotonic groups. Although gross pathologic lesions were found in 32% of the hypertonic groups and in fewer than 5% of the isotonic groups, this difference was not statistically significant. Equal bone changes were found in the slow- and rapid-infusion groups. CONCLUSION: The rate of intraosseous infusion and the osmolarity of the infused fluid did not appear to be related to any gross pathologic or histologic cellular or marrow changes or to any clinical complications in animal development in this study.

[Nerve transplantation in the central nervous system: a strategy for inducing nerve fiber regeneration in lesions of the brain and spinal cord]. / Transplantation de nerf dans le système nerveux central: une stratégie pour provoquer la repousse des fibres nerveuses lors de lésions du cerveau et de la moelle épinière.

Nerve grafts have long been used as a reconstructive strategy in the human peripheral nervous system. In the nervous system (brain and spinal cord), peripheral nerve grafts have been used experimentally for promoting axonal regeneration in lesioned pathways. Peripheral nerve grafts play the role of physical and trophic supports that are favourable for the regeneration of central fibres that normally present only abortive regeneration in adult mammals. On the basis of several experimental models (axonal regeneration of retinal ganglion cells, respiratory neurones, ...) it has now been established that central fibres that have regenerated within the nerve grafts retain their ability to transmit normal nervous information and can make functional synaptic contact with a target. If such a strategy is not yet used in man, it nevertheless constitutes a promising approach for the investigation of the central nervous system plasticity, and could be useful in the treatment of spinal cord injuries.

Central respiratory neuronal activity after axonal regeneration within blind-ended peripheral nerve grafts: time course of recovery and loss of functional neurons.

Autologous segments of peroneal nerve were implanted into the medulla of adult rats to induce axonal regeneration of central neurons axotomised during the grafting procedure. Grafts were inserted in the midline--where respiratory axons decussate--or laterally, either in the nucleus tractus solitarius or in the nucleus ambiguus, close to respiratory cell bodies. The distal part of each graft was left unconnected (blind-ended graft). Between 2 and 30 months post-implantation, unit recordings from single fibres were made from small strands teased from the grafts to investigate activity of neurons regenerating axons. Spontaneous respiratory and non-respiratory activity was present only in grafts examined between 2 and 6 months post-implantation. Respiratory units had discharge patterns identical to those of normal inspiratory or expiratory neurons; their responses to lung inflation and asphyxia were also similar to those of central respiratory neurons. No spontaneous activity was present in the grafts examined 7-30 months post-implantation. Moreover, asphyxia, which normally enhances the activity of central respiratory neurons, failed to elicit activity. These results were similar in all grafts, regardless of the site of implantation. The presence of spontaneous activity only between 2 and 6 months post-implantation indicates that once axonal growth of respiratory neurons is stopped within blind-ended grafts, those neurons still exhibited normal functional properties for 3 months. The absence of activity 6 months after grafting suggests that loss of functional regenerating respiratory neurons does not occur progressively and follows an "all or nothing" rule within blind-ended grafts.

Typing and screening of blood from intraosseous access.

STUDY OBJECTIVE: To determine if intramedullary aspirate from intraosseous needle placement can be used as a source for evaluating blood compatibility. DESIGN: A prospective, nonrandomized, crossover study. SETTING/PARTICIPANTS: Patients admitted to the hematology/oncology service undergoing bone marrow aspiration for medical purposes. INTERVENTIONS: Patients had simultaneous samples of bone marrow aspiration from the posterior iliac crest and peripheral venous blood drawn and sent for typing and screening. MEASUREMENTS AND MAIN RESULTS: The paired samples were evaluated for ABO and Rh typing as well as the presence of human leukocyte activity by evaluating the reaction strength between the marrow and venous samples. RESULTS: No differences were seen in the reaction strength between the paired samples in any subjects for ABO and Rh typing (P = .90, yielding beta = .0523). In addition, human leukocyte activity was detected in both the marrow and venous samples in one patient. CONCLUSION: Bone marrow aspirates following intraosseous infusion can be used for accurate and reliable typing and screening of blood.

Axonal regeneration from central respiratory neurons of the adult rat into peripheral nerve autografts: effects of graft location within the medulla.

In adult rats, autologous segments of the peroneal nerve were implanted into the medulla oblongata at the level of the obex either on the midline (midline grafts, n = 4), where respiratory axons decussate, or on the left side (lateral grafts, n = 5) in the area of the respiratory cell bodies. Several months after the graft implantation, spontaneous unitary activities (n = 225) were recorded within the grafts and were found to arise from both central respiratory (R, n = 72) and non-respiratory (NR, n = 153) neurons which were giving off regenerated axons along the nerve grafts. The graft reinnervation by respiratory axons was found to be significantly more abundant within the medullary lateral grafts than within the midline grafts. This finding offers further support of the conclusion that the reinnervation of grafts by axons from central neurons is enhanced when the graft is placed proximally to the cell bodies.

Functional significance of the dorsal respiratory group in adult and newborn rats: in vivo and in vitro studies.

The involvement of the dorsal part of the medulla (the so-called dorsal respiratory group: DRG) in the networks participating in respiratory function was investigated in newborn (in vitro) and adult (in vivo) rats. In the dorsal part of the medulla of the isolated brainstem of newborn rats, no respiratory neurons were found and stimulations or lesions neither modified nor suppressed the respiratory output. On the contrary, similar experiments suggest that sites in the ventral medulla have a fundamental importance for respiration. In adult rats, lesion of the DRG areas by electrocoagulation induced transient changes in respiratory timing, and resulted in a significant decrease in the amplitude of the contralateral phrenic output. These results suggest that the dorsal part of the medulla is not involved in controlling respiratory activity in the newborn rat. In adults, no definite conclusion can be reached, but the functional role of the DRG, if any, is probably restricted.

Effects of N-methyl-D-aspartate (NMDA) antagonist MK-801 on breathing pattern in rats.

In anaesthetized, bivagotomized and artificially ventilated rats, the respiratory effects of systemic injection of MK-801, a non-competitive N-methyl-D-aspartate antagonist, were studied. In all the experiments (n = 11), the injection increased the inspiratory duration and decreased the expiratory duration. In 4 experiments, the inspiratory duration was drastically lengthened, resulting in an apneustic-like breathing pattern. These results demonstrate that apneusis is difficult but possible to induce in rats and suggest that termination of inspiration is controlled via central mechanisms in which NMDA-like receptors are involved.

Comparison of serum phenobarbital levels after single versus multiple attempts at intraosseous infusion.

Serum drug levels from a single intraosseous attempt in nontraumatized bone have proven comparable to levels from IV drug infusions. However, in the clinical situation, inexperienced personnel may make multiple intraosseous attempts, which could allow significant extravasation from multiple intramedullary entrance sites. Serum drug levels arising from multiple intraosseous attempts in traumatized bone were compared with those arising from single intraosseous attempts in nontraumatized bone. We administered phenobarbital to 24 dogs randomly divided into single- (11) and multiple-attempt (13) groups. In the multiple-attempt group, we created three intramedullary insertion sites in a linear fashion and infused through only the central site. In the single-attempt group, only a single infusion site was created. Phenobarbital then was infused into the intramedullary space, and central venous phenobarbital samples were collected at one-, three-, six-, and ten-minute intervals. The single-attempt group attained significantly higher serum phenobarbital levels at each interval compared with the multiple-attempt group (P less than .0001). Therefore, to be an effective mode of therapy, it is critical to achieve single-attempt intraosseous needle placement for intraosseous infusion.

Pneumotaxic centre and apneustic breathing: interspecies differences between rat and cat.

Pontine influences on the breathing pattern were studied in rats using either in vivo experiments in anaesthetized adult animals or in vitro experiments in newborn preparations. In cats, after anaesthesia and bivagotomy, pontine transection has been described as evoking an apneustic pattern of breathing (long sustained inspiratory discharges interrupted by short expiratory pauses). In rats, after anaesthesia, bivagotomy and pontine transection, apneustic patterns of breathing were not observed, either in vivo or in vitro. These results suggest interspecies differences between rat and cat in the pontine influences on the medullary respiratory generator.

Analysis of growth plate abnormalities following intraosseous infusion through the proximal tibial epiphysis in pigs.

Intraosseous infusion has become an increasingly popular technique for vascular access in critically ill or injured children. Continuing acceptance of this procedure by physicians and possibly by prehospital personnel may lead to inadvertent placement through the immature growth plate. In our study, we intentionally penetrated the epiphyseal plate with the intraosseous needle and infused fluids in order to observe what complications, if any, might arise from this procedure. Twenty pigs 3 to 4 weeks old had a bone marrow aspiration needle introduced into the medullary cavity through the tibial epiphysis under fluoroscopic visualization. Sodium bicarbonate at 2 mEq/kg (n = 10) or 0.9 normal saline at 2 mL/kg (n = 10) was infused through the intraosseous needle. Radiographs of the involved growth plates were taken at two months and six months after infusion. No growth disturbances or growth plate abnormalities were detected clinically or radiographically through the rapid growth phase of the porcine tibia. Therefore, we believe that intraosseous infusion is a safe method of alternative vascular access associated with no significant growth defects despite injury to the developing growth plate from placement and infusion.